Variable range marking circuit with signal modulation for display identification



May 17, 1960 l.. s. MICHELs VARIABLE RANGE MARKING CIRCUIT WITH SIGNAL MODULATION FOR DISPLAY IDENTIFICATION 2 Sheets-Sheet 1 Filed Feb. 21, 1955 Y wr c er May 17, 1960 l.. s. MICHELs 2,937,339

VARIABLE RANGE MARKING CIRCUIT WITH SIGNAL NoDuLATIoN RoR DISPLAY IDENTIFICATION Filed Feb. 21, 1955 2 Sheets-Sheet 2 VARIABLE RANGE MARKING CIRCUIT WITH SIGNAL MODULATION FOR DISPLAY IDEN- TIFICATION Lawrence S. Michels, Inglewood, Calif., assignor to Giliillan Bros. Inc., Los Angeles, Calif., a corporation of California f l' Application Februaryzl, 19'5'5, Serial No. 489,360 10 Claims. (Cl. `328-189) i This invention relates to a variable range marking circuit with signal-,modulation for display identification and, v more particularly, to a variable rangek marking circult which may be utilized for providing a composite visual display for a radar or ground approach system where several range intervals maybe madey available through the same apparatus without confusion.

In many radar applications it is necessary to provide a 'variety of scanning ranges so that the precision of .the Adisplay may be increased as the Vtarget nears the scanning @manner are readily distinguished since the number of range marks therein generally differs substantially. Thus', the conventional technique introduces no confusionlsin'ce the short and long ranges appear upon diierent 'display devices and different displays in the same range have a considerable variation in the number of Vrange marks.

l However, it is apparent that the conventional technique requires a certain duplication in apparatus since twoddis- .play devices must be provided to cover the short and long ranges.

Moreover, the standard technique generally requires three types of range marking circuits for generating l, 2 and 5 mile markers. The l and 2 mile `ma'rkersmay be Y, utilized for the short range displaysV and the v5V mile markers yfor the long range displays. Y

Where economy is of theessence, the' conventional technique is lnot suitable since it becomes desirable to utilize a single display for both short and 'long ranges. In this situation, then, the standard technique becomes yconfusing Whenever the number of markers occurring in theentire display is the same. Thus a 20 mile display with 2 mile markers would appear identical tor'a l0 mile display with lmile markers. 'Y Y Furthermore, Vit is desirable to minimize the number of range marking'circuitsrequired sol that only two such .circuits need be utilized suchas a .units marking circuit,

or one mile marker, and' a multiple units marking circuit such as a 5 mile marker.

The present invention solves this problem in an eflicient mannerv and obviates theA necessity for providing V,separate displays for short and longranges 'to avoid conf fusion.V Furthermore, the same means which introduces a distinguishing characteristic between the short and long range displays also `provides additional marking signals without separate range marking circuits.

According vto the present :invention 'the short range, or

precision scales, include -rangewmarkers of varying in- .,tensities, the signals being derived ,through :a ,count f United States Patent O i Y2,937,339 Patented May V.17,

and modulates such signals in amplitude in `accordance with a predetermined count-down function. Thus, in a simple arrangement, a count-down of 2 maybe performed so that successive range marks in the short range scale appear alternately in varying intensity. In this situation, then, a short range scale of 5 or 10 miles includes intensified marks at even intervals of miles such as 0, 2, 4, etc., and reduced intensity marks at odd intervals of miles. y i

The long range scales then include a 'fewer :number of, or no variations in intensity and may, for example, include only 5 mile markers without any variation. In

this manner, then, the utilization of the same display r device to provide short range scales of 5 andV 10 miles and long range scales of 20 and 40 miles causes no confusion since the short range scales are readily `identified through the varying intensity of the markers. Moreover, the alternate variation of marker intensity effectively serves as a double range marking system so that, in the case discussed above, a single 1 mile markerprovides both l and 2 mile marking signals.

In this manner a single display may be utilized to provide a plurality of scales andonly two range marking circuits are required. The invention may be extended, of course, to utilizations where the count-down operation is more complicated. For example, three die'rent ranges may be provided on the samedisplay where the shortest range includes three gradations of Yintensity in the range marking signals, the varying modulation being achieved through a scale-of-3r count; theintermediate range display may include two gradations in inten- Accordingly, it is an object of the present invention to provide a variable range marking circuit'rwhich may be utilized to provide a plurality of range displays without confusion. v I

Another object of the invention is to provide a range marking circuit with signal modulation for display identification 'where short and long range displays may be shown on the same device Without resulting in confusion Where the number of range marks ris the same for different displays. Y

A further object of the invention is to provide a variable range marking circuit wherein only a units and multiple units marking circuit is vrequired,.the units marking being count-down modulated to provide variation in amplitude between successive marks.

Yet another object of the invention is toVprovide a circuit allowing a variety of scanning range `displays of varying precision with a minimum of circuits' and without confusion between displays. p

Still another object of the invention is to provide an economical range marking circuit wherein display identiadvantages thereof, will be better understood from'the following description considered in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are Vfor the' purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. l is a block diagram of one form of variable range marking circuit with signal modulation for display identification according to the present invention;

Fig. la is a composite set of waveforms of various signals which appear in the embodiment of Fig. 1 in a typical operation;

Fig. lb shows the general appearance of the display of the marking pulses of Fig. 1a for respective scales; and

Fig. 2 is a schematic diagram of a speciiic circuit arrangement which may be utilized in the embodiment of Fig. l.

Reference is now made to Fig. 1 wherein there is shown a circuit for producing range marking pulses suitable for display through the same means, Without confusion between displays representing different scales. As shown in Fig. 1, the circuit comprises a variable range gated oscillator 100 which receives a range gate signal A and produces output signal B at a repetition rate corresponding to the interval between range marking signals desired.

Signals thus produced by oscillator 100 are applied to a pulse amplifier and amplitude modulator stage 200 which produces modulated output signals C having amplitudes controlled in accordance with a signal D, produced by an amplitude control circuit 30). Control circuit 300 receives a signal C for each occurrence of a signal C and then is operative to count down between successive signals C' by a predetermined amount to produce an amplitude control signal specifying a predetermined arrangement of intensity gradations among signals C. It will be understood that signals C' may be the same as signals C or B or any other signals indicating the time of occurrence of signals C.

The embodiment of Fig. l also includes a mixing circuit 400 which receives signals C and other signals such as cursor signals and produces a composite set of marking output signals. It will be understood, however, that circuit 400 does not formA an essential part of the invention. Y

The basic principles of the invention may. be better understood by considering a typical operation such as is depicted in Figs. 1a and 1b. In these figures three range scales are to be marked, provision being made so that the marking of the scales may be achieved through the same display arrangement. In the particular illustration, the scales of 10, 20 and 4() miles have been selected, the 10 and 20 mile scales including l and 2 mile markers and the 40 mile scale including 5 mile markers.

The Waveform notation utilized in Fig. la has been selected to allow the utilization of the same letters A, B, C and D to represent the same waveform for each of the three situations, a subscript l, 2 or 3 being utilized to indicate the 10, `2() and 40 mile scale representations, respectively. Thus the waveforms A1, B1, C1 and D1 represent: the range gate signals A; the oscillator signals B; the pulses C; and the control signals D, during the l mile scale marking operation.

Referring to Fig. la then it will be noted that in the assumed illustrative case oscillator 100 is variable between two types of markers. The first marker may be considered to be a units marker, or 1 mile marker, and the second marker a multiple units marker, or 5 mile marker. Thus in the l0 and 20 mile scales the oscillator is actuated in accordance with a range selection signal, which may be achieved through a mechanical switching action, to produce units marking signals; and during the 40 mile scale operation oscillator 100 produces signals B marking 5 mile intervals.

Although a multitude of diiferent types of control signals D may be utilized to specify distinguishing amplitude characteristics in signal C it is assumed, as an illustration, that signal D is a two level signal. This signal has a relatively high level prior to the receipt by circuit 300 of circuit C' and thereafter has a lowered level for a period which is assumed as an illustration to be somewhat greater than a l mile marking period, but less than a 2 mile marking period.

The amplitude of signal D then controls the amplitude of signal C so that in the ca se of the 10 and 20 mile scales signals C marking even mile intervals 0, 2, 4, etc., assume a relatively large amplitude providing a corresponding intensified range mark on the respective display of Fig. lb; and odd mile marking signals C, in these displays, assume a lower amplitude corresponding to the lower amplitude of control signal D, and the mark in the respective display of Fig. 1b appears at a lower intensity.

At this point it may be noted that the display arrangement of Fig. lb is not intended to represent a particular type of radar presentation such as a BV or P.P.I. display. The important thing to note is the simple manner in which various range signals may be distinguished and that eiectively additional range marking signals are achieved due to the differing intensity between marks, without the necessity of additional range-gated oscillator means. It should further be understood that the waveforms of Fig. la represent only a single range-gated interval. Consequently, in a typical application such as the utilization of the invention to provide a B display, the signals provided represent only a series of horizontal dots at respective range intervals, the dots being modulated in intensity in accordance with the preselected modulation function.

The other important thing to note in this general description is that the amplitude control circuit 300 does not function to modulate any of the 5 mile markers in the 40 mile scale since the count down function has been selected so that control signal returns to its relatively high amplitude following the receipt of a signal C before the end of a 2 mile marking period thereafter. Thus the 40 mile scale could include 2, 3 or 4 mile markers in place of the 5 mile marking signals and the 40 mile scale still would be readily distinguishable from either the l0 or 20 mile scales in that the variation in marking intensity is absent therein.

Thus one utilizing this display arrangement may switch to any of the range scales and may easily detect the difference therebetween due to the variation in display gradations between short and long range scales, and due to the substantial difference in numbers of range marks in range scales of the same order. Further, it will be noted that the signal modulation approach provides a convenient manner of effectively introducing additional markers without the necessity of additional range-gated oscillators or additional circuitry to provide further selections in the oscillator already available.

A specific circuit arrangement for practicing the invention is shown in Fig. 2 where particular values of circuit elements which may be employed are indicated; While the circuit arrangement shown is preferred for providing range marks alternating in intensity, every other mile, it will be understood that other arrangements may be preferred if diierent types of signal modulation are desired for display identification.

Referring now to Fig. 2, it is noted that variable range gated oscillator includes an input clamping stage 110 having a triode type 5814 connected as a diode so as to prevent the input signal applied to oscillator stage 120, which follows, from exceeding ground potential.

Oscillator stage may be considered to be a conventional Hartley oscillator including two tuned circuits 120-1 and 120-2 tuned to provide 1 and 5 mile range marking signals respectively; The conventional Hartley feedback circuit between the center tap coil and the cathode of the oscillator stage is achieved through a doublepole-double-throw switch 122 which connects the selected tuned circuit to the cathode of tube T120, a suitable tube being indicated as a. one-half section of type 12AT7. Tuned circuit 120-1 or 120-2 is gated in response to range gate signal A applied to stages T121 and T122,

l which 'fn-Qimmy Suppress any1 Ioscillation ;therein :until receipt .ofsignal A.' vf While control circuit 300 may assume a multitude of differentformsgdepending upon the type of modulation desired, lit -is f shown in a vconvenient arrangement as 'including asnglestablestate-multivibrator stage 310 and an routput amplifier'stage 320. Theimportant thing to .befnotedis'that-thetime constants of stage 310 are l selected so V that the time required for the return of stage 310gto its'initial--stable state after receipt of a signal C from-stage 200 is `selected Vto exceed -the time between units or lfrnile marking signals provided by oscillator 120, but-is less than a 2 -mile marking interval.

' 'The operation of stage 310 may be better understood lin terms-of the'specific operation of certain circuit elements therein. 'For this purpose assume that stage 310 is unactuatedfuntil a signal C' is received. The receipt of afsignal C causes a negative signal to be developed by input tube T311, which passes through capacitor C311 and cuts off Atube T312, causing `-an increased amplitude signal to'be applied to tube T 321 in amplifier 3,20. Am-

plifier z321) ythen Vproduces a reduced level output signal in :response thereto, the duration of which corresponds to the length vof vthe unstable 4state period of multivibrator 310. l l

As is well known, ythe length of vthe unstable state of a 'multivibrator such -as 'stage 310 depends upon the time required vfor capacitor`C311 to discharge sufficiently so that -tube 'T312 Vmay Aagain conduct, returning the amplitude control signal D again to a high level.

`In-operation'thevn multivibrator stage 310 is triggered vtoastate-controlling the production of a control signal D of decreased amplitude in response to alternate signals 'C'. Once having been triggered to its unstable state, multivibrator 310 is then not responsive to the following signal C and returns to its initial state after a time specified by the circuit 'constants as discussed above..v

Essentially, .the arrangement shown is a circuit providing a count-down function of 2 where the multivibrator counts in a binary fashion and controls the modulation in amplitude of every other marking signal. However, it may be convenient to utilize other count-down functions, as forexample may be achieved through a ternary counter. This' operation may be achieved through an integrating'countingcircuit such as may employ capacitorszfor energystorage, typical arrangements beingjfound f in United States Patent No. 2,619,618 for Energy Storage Counter by Bernard Adler issued November 25, 1952;

` and United-States Patent No. 2,686,008 for Counting and Scaling Circuits by William C. Davidon issued August l0, 1954.

It will be noted that a mixing circuit 400 is shown, although it does not form an essential part of the invention. This circuit may be utilized to combine the modulated range marking signals provided by the present invention with other signals such as cursor signals provided through other means.

From the foregoing description it is apparent that the present invention provides an efficient means for generating marking signals having variations in modulation for display identification. According to the basic concept of the invention signals such as C' are effectively counted and corresponding marking signals are modulated according to a predetermined identification function so that signals representing a plurality of different ranges may Yzbeiltilized :to `controlthe :same display 'without' con# fusion.

A specific circuit arrangement hastbeen'showniniorder to illustrate a simple technique for Vdisplay:identification where a count-downoperation in the scale of.2iisspecified.` f Y tem including ,means for 'displaying Ltar"get-.'representi'rig -f signals indicating .the position of the targetlin 'theco'rresponding range interval; a signal generator vfor producing modulated marking pulses representing ra'nge marks in a'selected range interval, themodulation of 'thepulses being selected to distinguish the displays fof different range intervals, said signal 'generator comprisingfmeans vfor producing vmarking pulses selectively representing either units or multiple units range marks; means responsiveto said marking pulses `for producing a modulating icontrol signal having at least two signal levels wherethe-difference in the signal levels corresponds to 'difference in intensity desired between said modulated pulses,said second means including a device for maintaining one of said signal levels fora predetermined period coextensive with the occurrence of a predetermined number of units marking pulses; and third means responsive 'tofsa'id marking pulses and to said modulating control signals for producing the modulated range marking pulses where'the variation in intensity between successive signals'is specified by said modulation control signal. 1

2. The generator defined in claim l wherein said third means includes a count down circuit for producing a modulation control signal at a frequency which lis reduced from the frequency of repetition of the'units .range pulses by a predetermined amount. Y

3. The generator defined in claim 2 wherein said p redetermined amount is selected so that alternate units marks are intensified but successive multiple units marks are not intensified. w

v4. A device for producing range-markingVpulsesisuitable for display through the same means withoutcon- 'fusion between displays representing' diierent range scales, .said device comprising: a variable frequency 'o'scilla-tor actuable to produce first output .signals having a repetition Yrate representing a range increment; an amlpliiier for receiving said first output signals andpro- -ducing `modulated second output signals having .respective amplitudes determined by the amplitude of areceived modulation control signal; and an amplitude con-trol circuit .coupled to said Vamplifier and responsive to said `second output `signals for producing the modulation control signal in accordance with a predetermined countdown function distinguishing the various range scales, said amplifier being ya blocking oscillator `circuit including a pulse transformer having primary and secondary windings and an electron discharge devicehaving an anode coupled to one end of said primary winding; said amplitude control signal being applied to the other end of said primary winding.

5. A device for producing range-marking pulses suitable for display through the same means without confusion between displays representing different range scales, said device comprising: a variable frequency os` cillator actuable to produce first output signals'Y having a repetition rate representing a range increment; an amplifier for receiving said first output signals and producing modulated second output signals vhaving respective amplitudes determined by the amplitudesof a received modulation control signal; and an amplitude con-v trol circuit coupled to said amplifier and responsive to said second output signals for producing the modulation control signal in accordance with a predetermined countdown function'distinguishing the various range scales, said amplitude control circuit including `a single state multivibrator having a return time constant selected to count-down from the repetition rate of the selected frequency of said variable frequency oscillator source to present a predetermined selected scale.

6. A device for producing range-marking pulses suitable for display through the same means without confusion between displays representing different range scales, said device comprising: a variable frequency oscillator actuable to produce first output signals having a repetition rate representing a range increment; an ampliier for receiving said first output signals and producing modulated second output signals having respective amplitudes determined by the amplitude of a received modulation control signal; and an amplitude control circuit coupled to said amplifier and responsive to said second output signals for producing the modulation control signal in accordance with a predetermined countdown function distinguishing the various range scales, said variable frequency oscillator producing at least two series of xed output signals representing one and live mile range markers, respectively, said amplitude control circuit including means for producing a control signal specifying a reduced amplitude for alternate second output signals representing one-mile markers, whereby short-range display such as ve or ten mile scales include one-mile markers of alternate gradations and longrange scales such as twenty or forty miles, including only live-mile markers.

7. A device for selectively generating at least two different sets of marking pulses for an indicator to produce visual representations thereon of scales which differ considerably in appearance, said device comprising: a source for periodically producing output pulses at least at two substantially constant, but different repetition frequencies; and modulation means responsive to an output signal of said source of only one of said two frequencies for changing the amplitude of at least every nth one of said output pulses to be the same amplitude as each successive nth output pulse, but to be different from the amplitude of at least one other of said output pulses in each successive group of n pulses, where n is any positive integer larger than unity.

8. A device for selectively generating at least two different sets of marking pulses for an indicator to produce visual representations thereon of scales which differ considerably in appearance, said device comprising: a source for producing alternating output signals at least at two substantially constant, but different frequencies; modulation'means responsive to said alternating output signals for generating output pulses at two different repetition rates corresponding to said two frequencies, respectively; and amplitude control means responsive to only one of Cil said two alternating output signals for changing the amplitude of at least every nth one of said output pulses to be the same amplitude as each successive nth output pulse, but to be different from the amplitude of at least one other `output pulse in each successiveV group of n pulses, where n is any positive integer larger than unity.

9. A device for selectively generating at least two different sets of marking pulses for an indicator to produce visual representations thereon of scales which differ considerably in appearance, said device comprising: a source for producing alternating output signals at least at two substantially constant, but different frequencies; modulation means responsive to said alternating output signals for generating output pulses at two different repetition Arates corresponding to said two frequencies, respectively; and amplitude control means responsive to only one of said two alternating output signals for changing the amplitude of at least every nth one of said output pulses to be the same amplitude as each successive nth output pulse, but to be different from the amplitude of at least one other output pulse in each successive group of n pulses, where n is any positive integer larger than unity, said amplitude control means being inoperative to amplitude modulate output pulses having a repetition rate corresponding to the other of said frequencies.

10. A device for selectively generating at least two different sets of marking pulses for an indicator to produce visual representations thereon of scales which differ considerably in appearance, said device comprising: a source for producing a lirst alternating output signal of a sub stantially higher frequency and a second alternating output signal of a substantially constant lower frequency; modulation means responsive to said alternating output signals for generating output pulses at higher and lower repetition rates corresponding to said higher and lower frequencies, respectively; and an amplitude control circuit including a monostable multivibrator having -a time constant greater than the reciprocal of said higher repetition rate and less than the reciprocal of said lower repetition rate, said amplitude control means being responsive only to said lirst and other alternating output signals having frequencies greater than the reciprocal of said multivibrator time constant for changing the amplitude of at least every nth one of said marker pulses to be the same amplitude as each successive nth output pulse, but to be different from the amplitude of at least one other in each successive group of n pulses, where n is any positive integer larger than unity.

References Cited in the le of this patent UNITED STATES PATENTS 2,425,330 Kenyon Aug. 12, 1947 2,564,006 Haworth Aug. 14, 1951 2,680,210 Miller et al. June 1, 1954 2,693,500 Cooper Nov. 2, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2,931,339 May 17g 1960 Lawrence S., Michel-s It is hereb5'r certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1,` line 39, after "devices" insert a Gemma@7 column 3, line 75, for "circuit" read signal m5 column 8 line .31

before '"higher'nf insert constant (SEAL) Attest: ERNEST W. SWIDER XXfXXXX/XXNI Attesting Officer ARTHUR W. CROCKER Acting Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORREU1`I01\I Patent m0 2,93%339 May 17g 1960 Lawrence S., Michel-s It is hereby certified that error appears in theprntedspecification of the above 'numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l, line 39, after "devices" insert a comma; eolumn 3, line `'75, for "circuit" read f signal me; column 8,. line 3l, before "higher" insert fconstant Signed and sealed this 4th day of April 1961..,

(SEAL) Attest: ERNEST W. SWIDER XMLXXXMXM ARTHUR W. CROCKER Attesting Oicer Acting Commissioner of Patents 

